We have all been subject to a selection of ads appearing down the side of our email client or on other websites that conveniently show us ads relating to products or websites we have previously visited. This may at first seem purely like a coincidence, but after a few times people tend to catch on that something quite clever is being used.
Many companies now collect and store data about our activity on the web. From searches we make to products we view and purchase. This data is used for statistical purposes but also to allow companies to target you specifically with ads you are more likely to click on.
There has been uproar recently with many people feeling that this is an invasion of their privacy. You can turn off Cookies or chose not to visit site that store this information but this can be frustrating and also quite technical to do. I think this is something we are all going to have to get used to as I think it will become used more and more.